The present invention relates to an image-pickup apparatus which performs autofocus (AF) by a so-called TTL phase difference detection method, and more particularly to an image-pickup apparatus which has a color measurement function used for light source detection.
In the TTL phase difference detection method, a pair of images formed by light that has passed through an image-pickup lens are photoelectrically converted by a light-receiving element for focus detection such as an image sensor, and a defocus amount of the image-pickup lens is calculated based on a displacement amount (phase difference) of the pair of images. Most of the light-receiving elements used for the focus detection are constituted of P-N junction type photodiodes. Their sensitivities extend from a visible wavelength region to a near-infrared wavelength region. This extension enables use of light of the near-infrared wavelength region as assist light irradiated to an object when the focus detection is performed for a dark object.
The image-pickup lens is generally designed so that chromatic aberration can be reduced in the near-infrared wavelength region. In many cases, however, the chromatic aberration is not satisfactorily corrected in the near-infrared wavelength region. Consequently, a proportion of near-infrared light relative to visible light varies among a case where the object is illuminated with sunlight, a case where the object is illuminated with light from a light source of a low color temperature such as a tungsten lamp, and a case where the object is illuminated with light from a light source of a high color temperature such as a fluorescent lamp, which causes different focus detection results. In other words, even in the case of objects equal in distance, the focus detection result varies depending on type of the light source, which disables satisfactory focus control.
To solve such a problem, it is necessary to detect (determine) the type of the light source and to correct the focus detection result based on the detection result.
Japanese Patent Laid-Open No. 2003-241064 discloses an image-pickup apparatus which determines a color of an object, i.e., an achromatic color, blue, green, or red, by using three photometry/color measurement sensors including primary color filters of RGB, and corrects a focus detection result based on the determination result. This determination result is also used for exposure correction.
However, the photometry/color measurement sensor disclosed in Japanese Patent Laid-Open No. 2003-241064 is constituted by using three light-receiving elements different from one another in position in an in-plane direction of a light entrance surface. Consequently, unless a special optical system is provided which causes light fluxes from the same point of the object to similarly form images on the three light-receiving elements, light-receiving fields of the three light-receiving elements are different from one another. The difference in light-receiving field among the three light-receiving elements causes a case where identical images of the object are not formed on the three light-receiving elements depending on an object's shape (e.g., a thin line). In this case, a color of the object cannot be accurately determined, thereby reducing the accuracy of focus detection result correction or exposure correction. In contrast, provision of a special optical system to match the light-receiving fields of the three light-receiving elements increases the size of the image-pickup apparatus.